System and method for forming a seismic velocity model and imaging a subterranean region

Abstract

A method for forming an image of a subterranean region of interest, using an observed seismic dataset, a seismic velocity model and a simulated seismic dataset based in part, on the seismic velocity model is provided. This method includes forming trace pairs from the simulated and observed seismic dataset, wherein each of the trace pairs comprises of an observed trace and a simulated trace. An objective function is formed based on a penalty function and a phase cross-correlation between the observed and simulated seismic trace of each of the trace pairs. This method further includes determining an extremum of the objective function and a seismic velocity increment based on the extremum. The seismic velocity model is updated by combining the seismic velocity increment and the seismic velocity model and the image of the subterranean region of interest is formed based in part, on the seismic velocity model.

What is claimed is: 
     
       1. A method of forming an image of a subterranean region of interest, comprising:
 obtaining an observed seismic dataset for the subterranean region of interest, wherein the observed seismic dataset comprises a plurality of seismic source locations, a plurality of receiver locations, and an observed seismic trace for each pair of seismic source location and seismic receiver location; 
 obtaining a seismic velocity model for the subterranean region of interest; 
 simulating, using a computer processor, a simulated seismic dataset wherein the simulated seismic dataset comprises a simulated seismic trace for each pair of seismic source location and seismic receiver location based, at least in part, on the seismic velocity model; 
 forming, using the computer processor, a plurality of trace pairs from the simulated seismic dataset and the observed seismic dataset, wherein each of the plurality of trace pairs comprises an observed seismic trace and a simulated seismic trace; 
 forming, using the computer processor, an objective function based, at least in part, on a penalty function and a cross-correlation between the observed seismic trace and the simulated seismic trace of each of the plurality of trace pairs; 
 finding, using the computer processor, an extremum of the objective function; 
 determining, using the computer processor, a seismic velocity increment based, at least in part, on the extremum; 
 forming, using the computer processor, an updated seismic velocity model by combining the seismic velocity increment and the seismic velocity model; and 
 forming, using the computer processor, the image of the subterranean region of interest based, at least in part, on the updated seismic velocity model. 
 
     
     
       2. The method of  claim 1 ,
 wherein forming the objective function comprises:
 calculating a phase cross-correlation function between a first member of each trace pair and a second member of each trace pair; 
 determining a trace objective function for each trace based, at least in part, on a normalized integral of a square of the phase cross-correlation function for each trace pair multiplied by the penalty function; and 
 summing the trace objective function over the plurality of trace pairs. 
 
 
     
     
       3. The method of  claim 1 , wherein forming the plurality of trace pairs comprises:
 selecting a common seismic source location and a common receiver location; and 
 selecting, as a first member of each trace pair, the observed seismic trace from the observed seismic dataset and selecting, as a second member of each trace pair, the simulated seismic trace from the simulated seismic dataset, wherein both the first member of each trace pair and the second member of each trace pair have the common seismic source location and the common receiver location. 
 
     
     
       4. The method of  claim 1 , wherein the penalty function has an absolute magnitude that increases monotonically with lag from a minimum value. 
     
     
       5. The method of  claim 1 , wherein determining the seismic velocity increment comprises:
 simulating a forward propagated seismic wave for at least one of the plurality of seismic source locations; 
 determining an adjoint source for at least one of the plurality of trace pairs based, at least in part, on a difference between the observed seismic trace and the simulated seismic trace; 
 simulating, for at least one of the plurality of trace pairs, a backward propagated seismic wave generated by the adjoint source; 
 determining at least one seismic velocity gradient increment using an imaging condition based, at least in part, on the forward propagated seismic wave and the backward propagated seismic wave; 
 obtaining a seismic velocity gradient based, at least in part, on the at least one seismic velocity gradient increment; and 
 determining the seismic velocity increment by scaling the seismic velocity gradient based, at least in part, on the extremum of the objective function. 
 
     
     
       6. The method of  claim 5 , wherein obtaining the seismic velocity gradient comprises performing a gradient-based local search procedure based, at least in part, on a plurality of seismic velocity gradient increments. 
     
     
       7. The method of  claim 1 , further comprising:
 identifying a portion of the subterranean region of interest with a likelihood of containing hydrocarbons based, at least in part, on the image of the subterranean region of interest; 
 determining a well path through the subterranean region of interest based, at least in part, on the identified portion of the subterranean region of interest; and 
 drilling the well path using a drilling system. 
 
     
     
       8. A non-transitory computer readable medium storing instructions executable by a computer processor, the instructions comprising functionality for:
 obtaining an observed seismic dataset for a subterranean region of interest, wherein the observed seismic dataset comprises a plurality of seismic source locations, a plurality of receiver locations, and an observed seismic trace for each pair of seismic source location and seismic receiver location; 
 obtaining a seismic velocity model for the subterranean region of interest; 
 simulating, using a computer processor, a simulated seismic dataset wherein the simulated seismic dataset comprises a simulated seismic trace for each pair of seismic source location and seismic receiver location based, at least in part, on the seismic velocity model; 
 forming, using the computer processor, a plurality of trace pairs from the simulated seismic dataset and the observed seismic dataset, wherein each of the plurality of trace pairs comprises an observed seismic trace and a simulated seismic trace; 
 forming, using the computer processor, an objective function based, at least in part, on a penalty function and a cross-correlation between the observed seismic trace and the simulated seismic trace of each of the plurality of trace pairs; 
 finding, using the computer processor, an extremum of the objective function; 
 determining, using the computer processor, a seismic velocity increment based, at least in part, on the extremum; 
 forming, using the computer processor, an updated seismic velocity model by combining the seismic velocity increment and the seismic velocity model; and 
 forming, using the computer processor, an image of the subterranean region of interest based, at least in part, on the updated seismic velocity model. 
 
     
     
       9. The non-transitory computer readable medium of  claim 8 , wherein forming an objective function comprises:
 calculating a phase cross-correlation function between a first member of each trace pair and a second member of each trace pair; 
 determining a trace objective function for each trace based, at least in part, on a normalized integral of a square of the phase cross-correlation function for each trace pair multiplied by the penalty function; and 
 summing the trace objective function over the plurality of trace pairs. 
 
     
     
       10. The non-transitory computer readable medium of  claim 8 , wherein forming a trace pair from the simulated seismic dataset and the observed seismic dataset, comprises:
 selecting a common seismic source location and a common receiver location; and 
 selecting, as a first member of each trace pair, the observed seismic trace from the observed seismic dataset and selecting, as a second member of each trace pair, the simulated seismic trace from the simulated seismic dataset, wherein both the first member of each trace pair and the second member of each trace pair have the common seismic source location and the common receiver location. 
 
     
     
       11. The non-transitory computer readable medium of  claim 8 , wherein the penalty function has an absolute magnitude that increases monotonically with lag from a minimum value. 
     
     
       12. The non-transitory computer readable medium of  claim 8 , wherein determining the seismic velocity increment comprises:
 simulating a forward propagated seismic wave for at least one of the plurality of seismic source locations; 
 determining an adjoint source for at least one of the plurality of trace pairs based, at least in part, on a difference between the observed seismic trace and the simulated seismic trace; 
 simulating, for at least one of the plurality of trace pairs, a backward propagated seismic wave generated by the adjoint source; 
 determining at least one seismic velocity gradient increment using an imaging condition based, at least in part, on the forward propagated seismic wave and the backward propagated seismic wave; 
 obtaining a seismic velocity gradient based, at least in part, on the at least one seismic velocity gradient increment; and 
 determining the seismic velocity increment by scaling the seismic velocity gradient based, at least in part, on the extremum of the objective function. 
 
     
     
       13. The non-transitory computer readable medium of  claim 12 , wherein obtaining the seismic velocity gradient comprises performing a gradient-based local search procedure based, at least in part, on a plurality of seismic velocity gradient increments. 
     
     
       14. The non-transitory computer readable medium of  claim 8 , the instructions further comprising functionality for:
 identifying a portion of the subterranean region of interest with a likelihood of containing hydrocarbons based, at least in part, on the image of the subterranean region of interest; and 
 determining a well path through the subterranean region of interest based, at least in part, on the identified portion of the subterranean region of interest. 
 
     
     
       15. A system for forming an image of a subterranean region of interest, comprising:
 a seismic source to emit a radiated seismic wave; 
 a plurality of seismic receivers for detecting and recording an observed seismic dataset generated by the radiated seismic wave; and 
 a seismic processor configured to:
 obtain an observed seismic dataset for the subterranean region of interest, wherein the observed seismic dataset comprises a plurality of seismic source locations, a plurality of receiver locations, and an observed seismic trace for each pair of seismic source location and seismic receiver location; 
 obtain a seismic velocity model for the subterranean region of interest; 
 simulate a simulated seismic dataset wherein the simulated seismic dataset comprises a simulated seismic dataset wherein the simulated seismic dataset comprises a simulated seismic trace for each pair of seismic source location and seismic receiver location based, at least in part, on the seismic velocity model; 
 form a plurality of trace pairs from the simulated seismic dataset and the observed seismic dataset, wherein each of the plurality of trace pairs comprises an observed seismic trace and a simulated seismic trace; 
 form an objective function based, at least in part, on a penalty function and a cross-correlation between the observed seismic trace and the simulated seismic trace of each of the plurality of trace pairs; 
 find an extremum of the objective function; 
 determine a seismic velocity increment based, at least in part, on the extremum; 
 form an updated seismic velocity model by combining the seismic velocity increment and the seismic velocity model; and 
 form the image of the subterranean region of interest based, at least in part, on the updated seismic velocity model. 
 
 
     
     
       16. The system of  claim 15 , wherein forming the objective function comprises:
 calculating a phase cross-correlation function between a first member of each trace pair and a second member of each trace pair; 
 determining a trace objective function for each trace based, at least in part, on a normalized integral of a square of the phase cross-correlation function for each trace pair multiplied by the penalty function; and 
 summing the trace objective function over the plurality of trace pairs. 
 
     
     
       17. The system of  claim 15 , wherein forming the plurality of trace pairs comprises:
 selecting a common seismic source location and a common receiver location; and 
 selecting, as a first member of each trace pair, the observed seismic trace from the observed seismic dataset and selecting, as a second member of each trace pair, the simulated seismic trace from the simulated seismic dataset, wherein both the first member of each trace pair and the second member of each trace pair have the common seismic source location and the common receiver location. 
 
     
     
       18. The system of  claim 15 , wherein the penalty function has an absolute magnitude that increases monotonically with lag from a minimum value. 
     
     
       19. The system of  claim 15 , wherein determining a seismic velocity increment comprises:
 simulating a forward propagated seismic wave for at least one of the plurality of seismic source locations; 
 determining an adjoint source for at least one of the plurality of trace pairs based, at least in part, on a difference between the observed seismic trace and the simulated seismic trace; 
 simulating, for at least one of the plurality of trace pairs, a backward propagated seismic wave generated by the adjoint source; 
 determining at least one seismic velocity gradient increment using an imaging condition based, at least in part, on the forward propagated seismic wave and the backward propagated seismic wave; 
 obtaining a seismic velocity gradient based, at least in part, on the at least one seismic velocity gradient increment; and 
 determining the seismic velocity increment by scaling the seismic velocity gradient based, at least in part, on the extremum of the objective function. 
 
     
     
       20. The system of  claim 15 , wherein the seismic processor is further configured to:
 identify a portion of the subterranean region of interest with a likelihood of containing hydrocarbons based, at least in part, on the image of the subterranean region of interest; and 
 determine a well path through the subterranean region of interest based, at least in part, on an identified portion of the subterranean region of interest.